package written_examination;
import java.util.*;

public class Main_1126_1 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int w = scanner.nextInt();
        int h = scanner.nextInt();
        int[][] arr = new int[w][h];
        int count = 0;
        for(int i = 0;i < w;i++){
            for(int j = 0;j < h;j++){
                //等于 0 说明可以放蛋糕
                if(arr[i][j] == 0){
                    count++;
                    if(i + 2 < w){
                        arr[i + 2][j] = 1;
                    }
                    if(j + 2 < h){
                        arr[i][j + 2] = 1;
                    }
                }
            }
        }
        System.out.println(count);
    }
}
